1. Field of the Invention
The present invention relates in general to a fuel supply apparatus for an internal combustion engine of fuel injection type. In particular, the invention concerns a fuel supply apparatus of the type in which intake air quantity is detected by an air valve disposed within an intake conduit upstream of a throttle valve and adapted to be so controlled that pressure in a constant pressure chamber defined between the air valve and the throttle valve may be maintained constant, while fuel quantity to be supplied to the internal combustion engine is controlled by a fuel metering assembly interlocked with the air valve so as to be proportional to the intake air quantity.
2. Description of the Prior Art
The prior fuel supply apparatus of the above type includes an intake conduit leading to the engine and having a throttle valve disposed therein, an air valve disposed within the intake conduit upstream of the throttle valve to define an air pressure chamber between the throttle valve and the air valve in the intake conduit, control means for controlling the air valve so as to maintain the pressure prevailing in the air pressure chamber at a preset value, a fuel supply source of a constant pressure for supplying fuel to the intake conduit through a fuel feed channel, a fuel flow metering valve disposed in the fuel feed channel and interlocked with the air valve such that the area of fuel flow section of the fuel flow metering valve is so controlled as to be in proportion to the opening degree of the air valve, and a fuel pressure differential means for maintaining the pressure difference produced across the fuel flow metering valve at a preset value.
In accordance with the prior fuel supply apparatus constructed as mentioned above, the air-fuel mixture may be controlled to have a predetermined air-fuel ratio independent of operating speeds of the internal combustion engine during normal operation mode thereof, whereby purification of exhaust gas from the engine can be accomplished to a reasonable degree. However, difficulties are encountered in controlling the required quantities of fuel in the transient operation modes of the engine such as acceleration and deceleration modes. Further, such transient operations of the engine requires air-fuel ratios different from the one required in the normal steady operation in order to assure satisfactory operation performance and purification of the exhaust gas.